1. Field of the Invention
This invention relates to apparatus for applying gum to spaced locations on an envelope blank subsequent to its folding into a finished envelope, and more particularly, such an apparatus including means for sensing the absence of an envelope fed to the gumming apparatus so that the gumming apparatus is reduced inactive upon the sensing of such a condition to preclude gum from being applied to the envelope blank feed means, rather than the envelope.
2. Description Of The Prior Art
Blanks from which envelopes are formed are required to go through a gluing operation subsequent to folding and forming of the envelope blank. The gluing operation deposits gum or adhesive on the flap of the envelope and a spaced portion adjacent thereto on the body of the envelope and then dried. When the envelope is used, the flap is moistened and folded so that it will adhere to the gum deposited and dried on the body portion of the envelope.
Normally, the gumming apparatus comprises an endless belt for feeding the folded envelope blanks to a gum applying cylinder. The envelopes are each fed with their flap opened and parallel to the main body which the flap will overlie when closed. Gum is applied by a pair of spaced gummer pads on the circumference of a rotating cylinder at a gummer station. Rotation of the cylinder is controlled so that gum is applied to the flap and main body portion of the folded envelope blank as the blank on the endless belt passes beneath the gummer cylinder.
This is accomlished by driving the gummer cylinder with a gripper belt entrained about a pulley connected to the gummer cylinder at a rate will assure that the gummer pads on the cylinder are over the feed belt when the envelope blank passes therebeneath. This requires that the linear spacing of the envelopes on the feed belt be correlated to the rotational velocity of the gummer cylinder. The gripper belt is positioned above the feed belt so that as a gum is applied to the envelope, the gripper will firmly hold the lower portion of an envelope to the feed belt and then will advance it through subsequent operations performed by the envelope apparatus, such as drying the applied gum. The gripper belt will always drive the pulley connected to the gummer cylinder to apply gum to spaced locations on the envelope blank such as the flap and a spaced portion of the body of the envelope blank. If for any reason an envelope blank is not present as the gummer cylinder completes its circular movement, glue will be applied to the feed belt rather than the envelope blank. This may cause the feed belt to adhere to the gummer cylinder as it passes therebeneath or other portions of the envelope forming apparatus as well as adhereing to subsequent blanks fed on the belt. The apparatus must be stopped and the belt cleaned before the apparatus can be continued to be operated.
In order to avoid such a problem, the prior art has suggested the use of a first photocell for detecting the presence of the envelope blank on the feed belt and a second photocell for monitoring the angular position of the gummer cylinder and producing a second output signal when the gummer cylinder is in proper position to apply gum to the next envelope blank as it passes the gummer cylinder. Means are coupled to the first or second photocell outputs so that in response to a signal that an envelope blank is missing from the feed belt, the gummer cylinder is precluded from applying gum to the feed belt. Such a means is disclosed in the application of David L. Gingerich, Ser. No. 950,626 filed Oct. 12, 1978, entitlted "Envelope Forming Machine" and assigned to the same assignee as the assignee of the present invention. In this application, the means for incapacitating the gum applying cylinder includes means responsive to the absence of a combined signal from the first and second photocells for moving the feed belt away from the gum applying cylinder.
This solution is awkward in that a separate mechanism must be provided for moving the feed away from the gum applying element. The present invention offers an alternate solution for incapacitating the gummer cylinder in that the gum applying cylinder is provided with gum applying pads extending along its circumference for contact with the envelope blank which are precluded from rotating into contact with the feed belt upon the sensing of the absence of an envelope blank to be gummed on the feed belt.